The present invention relates to a development apparatus for use in an electrophotographic copying machine, for developing to a visible image a latent electrostatic image formed on a latent electrostatic image bearing member, by a developer carried by a developer transport member onto the latent electrostatic image bearing member.
A development apparatus of the type mentioned above for use in an electrophotographic copying machine or in an electrostatic recording apparatus is known. In such development apparatus, usually a two-component type developer comprising toner and carrier particles is employed, but a one-component type developer is occasionally employed in the development apparatus. In either case, it is necessary that the thickness of the developer layer carried on the developer transport member be small, since when the diameter of the carrier particles in the two-component developer is small, the thickness of the developer layer must be small. When a one-component type developer with high volume resistivity is employed, it is necessary that the developer be electrically charged by a development apparatus and, accordingly, the developer layer has to be extremely thin. Otherwise, only the surface portion of the developer layer, not the entire developer layer, is electrically charged.
Conventionally, in order to obtain a developer layer with the desired thickness, a doctor blade is employed as a developer layer control means for regulating the thickness of the developer layer on a developer transport member, which doctor blade is directed towards the developer transport layer and is capable of scraping excess developer from the developer transport member to regulate the thickness of the developer on the developer transport member. However, there is a limitation to the thickness of the developer that can be obtained by means of the doctor blade. Furthermore, when a thin developer layer is obtained by the doctor blade, it is necessary that the gap between the doctor blade and the developer transport member be small, and, if some foreign material happens to be mixed with the developer and the foreign material enters the small gap, the development cannot be done properly.
In order to prevent the above-mentioned disadvantage, a development apparatus capable of obtaining a layer of developer much thinner than the gap possible between a doctor blade, made of a magnetic material, and a developer transport member has been conventionally proposed. However, there is a practical limitation to the thickness of the developer that can be obtained by that development apparatus, and therefore it is extremely difficult to obtain a layer of developer with the desired thickness.